<title>Completely embedded optical fiber sensors</title>

Abstract

Due to their small size, light weight, geometric flexibility and their possible uses for monitoring various different physical parameters, optical fiber sensor technology offers numerous opportunities and advantages for instrumenting structures and materials for their analysis and control. While optical fiber sensors have advantages over conventional electric sensors, connectorization of optical fiber sensors to the supporting laser, detector and electronics has proven to be difficult. The conventional approach to connecting the embedded optical fiber sensors, bringing the optical fiber leads out of the material, creates obvious points of failure at the points where the fiber enters and exits the material, and greatly complicates the process of joining adjacent structural elements, each containing sensor fibers which must be connected. In this paper we demonstrate the possibility of having an optical fiber sensor system that can be completely embedded within composite materials. The fiber sensor as well as the supporting opto-electronic components required to launch and receive light into and from the fiber could be embedded in a panel, avoiding connector problems. Interaction with the electronics to obtain strain and vibration measurements from the fiber sensor was made via external antenna coils.

Free-space input and output coupling to an embedded fiber optic strain sensor: dual-ended interrogation via transmission

“…A more common in-plane approach is to extend a "pigtail" of optical fiber out of the edge of the structure and physically connectorize that free fiber end. 13,[15][16][17] A critical disadvantage of this approach is the fragility of the fiber where it enters or exits the structure. Various techniques have been applied to protect the fiber optic leads at the point of ingress/egress.…”

Free space optical coupling to completely embedded fiber Bragg grating sensors

“…A more common approach is to extend a "pigtail" of optical fiber out of the embedded structure and then physically connectorize that free fiber end. A critical disadvantage of this approach is the fragility of the fiber where it enters or exits the structure [10][11][12] . Kang et al [13] proposed an out-of-plane ingress/egress method to improve the survivability of the fiber pigtail.…”

Mirrored line-of-sight input nodes for embedded optical waveguides

“…SLANs may also permit design and manufacturing simplification, and enable redundant pathways and reconfigurable networks. 8 Because the fragility of optical fiber at the ingress/egress points creates a high probability of failure, [9][10][11][12][13] the major hurdle in implementing SLANs, particularly for optical communication, is connectorization. This connectorization problem can be eliminated by remotely interrogating embedded networks using, for example, graded index ͑GRIN͒ lenses to passively couple light into optical fibers.…”